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The following is the second version of the function return probe patches
I sent out earlier this week. Changes since my last submission include:
* Fix in ppc64 code removing an unneeded call to re-enable preemption
* Fix a build problem in ia64 when kprobes was turned off
* Added another BUG_ON check to each of the architecture trampoline
handlers
My initial patch description ==>
From my experiences with adding return probes to x86_64 and ia64, and the
feedback on LKML to those patches, I think we can simplify the design
for return probes.
The following patch tweaks the original design such that:
* Instead of storing the stack address in the return probe instance, the
task pointer is stored. This gives us all we need in order to:
- find the correct return probe instance when we enter the trampoline
(even if we are recursing)
- find all left-over return probe instances when the task is going away
This has the side effect of simplifying the implementation since more
work can be done in kernel/kprobes.c since architecture specific knowledge
of the stack layout is no longer required. Specifically, we no longer have:
- arch_get_kprobe_task()
- arch_kprobe_flush_task()
- get_rp_inst_tsk()
- get_rp_inst()
- trampoline_post_handler() <see next bullet>
* Instead of splitting the return probe handling and cleanup logic across
the pre and post trampoline handlers, all the work is pushed into the
pre function (trampoline_probe_handler), and then we skip single stepping
the original function. In this case the original instruction to be single
stepped was just a NOP, and we can do without the extra interruption.
The new flow of events to having a return probe handler execute when a target
function exits is:
* At system initialization time, a kprobe is inserted at the beginning of
kretprobe_trampoline. kernel/kprobes.c use to handle this on it's own,
but ia64 needed to do this a little differently (i.e. a function pointer
is really a pointer to a structure containing the instruction pointer and
a global pointer), so I added the notion of arch_init(), so that
kernel/kprobes.c:init_kprobes() now allows architecture specific
initialization by calling arch_init() before exiting. Each architecture
now registers a kprobe on it's own trampoline function.
* register_kretprobe() will insert a kprobe at the beginning of the targeted
function with the kprobe pre_handler set to arch_prepare_kretprobe
(still no change)
* When the target function is entered, the kprobe is fired, calling
arch_prepare_kretprobe (still no change)
* In arch_prepare_kretprobe() we try to get a free instance and if one is
available then we fill out the instance with a pointer to the return probe,
the original return address, and a pointer to the task structure (instead
of the stack address.) Just like before we change the return address
to the trampoline function and mark the instance as used.
If multiple return probes are registered for a given target function,
then arch_prepare_kretprobe() will get called multiple times for the same
task (since our kprobe implementation is able to handle multiple kprobes
at the same address.) Past the first call to arch_prepare_kretprobe,
we end up with the original address stored in the return probe instance
pointing to our trampoline function. (This is a significant difference
from the original arch_prepare_kretprobe design.)
* Target function executes like normal and then returns to kretprobe_trampoline.
* kprobe inserted on the first instruction of kretprobe_trampoline is fired
and calls trampoline_probe_handler() (no change here)
* trampoline_probe_handler() consumes each of the instances associated with
the current task by calling the registered handler function and marking
the instance as unused until an instance is found that has a return address
different then the trampoline function.
(change similar to my previous ia64 RFC)
* If the task is killed with some left-over return probe instances (meaning
that a target function was entered, but never returned), then we just
free any instances associated with the task. (Not much different other
then we can handle this without calling architecture specific functions.)
There is a known problem that this patch does not yet solve where
registering a return probe flush_old_exec or flush_thread will put us
in a bad state. Most likely the best way to handle this is to not allow
registering return probes on these two functions.
(Significant change)
This patch series applies to the 2.6.12-rc6-mm1 kernel, and provides:
* kernel/kprobes.c changes
* i386 patch of existing return probes implementation
* x86_64 patch of existing return probe implementation
* ia64 implementation
* ppc64 implementation (provided by Ananth)
This patch implements the architecture independant changes for a reworking
of the kprobes based function return probes design. Changes include:
* Removing functions for querying a return probe instance off a stack address
* Removing the stack_addr field from the kretprobe_instance definition,
and adding a task pointer
* Adding architecture specific initialization via arch_init()
* Removing extern definitions for the architecture trampoline functions
(this isn't needed anymore since the architecture handles the
initialization of the kprobe in the return probe trampoline function.)
Signed-off-by: Rusty Lynch <rusty.lynch@intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Now that PPC64 has no-execute support, here is a second try to fix the
single step out of line during kprobe execution. Kprobes on x86_64 already
solved this problem by allocating an executable page and using it as the
scratch area for stepping out of line. Reuse that.
Signed-off-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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In situations where a kprobes handler calls a routine which has a probe on it,
then kprobes_handler() disarms the new probe forever. This patch removes the
above limitation by temporarily disarming the new probe. When the another
probe hits while handling the old probe, the kprobes_handler() saves previous
kprobes state and handles the new probe without calling the new kprobes
registered handlers. kprobe_post_handler() restores back the previous kprobes
state and the normal execution continues.
However on x86_64 architecture, re-rentrancy is provided only through
pre_handler(). If a routine having probe is referenced through
post_handler(), then the probes on that routine are disarmed forever, since
the exception stack is gets changed after the processor single steps the
instruction of the new probe.
This patch includes generic changes to support temporary disarming on
reentrancy of probes.
Signed-of-by: Prasanna S Panchamukhi <prasanna@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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This patch moves the lock/unlock of the arch specific kprobe_flush_task()
to the non-arch specific kprobe_flusk_task().
Signed-off-by: Hien Nguyen <hien@us.ibm.com>
Acked-by: Prasanna S Panchamukhi <prasanna@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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The architecture independent code of the current kprobes implementation is
arming and disarming kprobes at registration time. The problem is that the
code is assuming that arming and disarming is a just done by a simple write
of some magic value to an address. This is problematic for ia64 where our
instructions look more like structures, and we can not insert break points
by just doing something like:
*p->addr = BREAKPOINT_INSTRUCTION;
The following patch to 2.6.12-rc4-mm2 adds two new architecture dependent
functions:
* void arch_arm_kprobe(struct kprobe *p)
* void arch_disarm_kprobe(struct kprobe *p)
and then adds the new functions for each of the architectures that already
implement kprobes (spar64/ppc64/i386/x86_64).
I thought arch_[dis]arm_kprobe was the most descriptive of what was really
happening, but each of the architectures already had a disarm_kprobe()
function that was really a "disarm and do some other clean-up items as
needed when you stumble across a recursive kprobe." So... I took the
liberty of changing the code that was calling disarm_kprobe() to call
arch_disarm_kprobe(), and then do the cleanup in the block of code dealing
with the recursive kprobe case.
So far this patch as been tested on i386, x86_64, and ppc64, but still
needs to be tested in sparc64.
Signed-off-by: Rusty Lynch <rusty.lynch@intel.com>
Signed-off-by: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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This patch adds function-return probes to kprobes for the i386
architecture. This enables you to establish a handler to be run when a
function returns.
1. API
Two new functions are added to kprobes:
int register_kretprobe(struct kretprobe *rp);
void unregister_kretprobe(struct kretprobe *rp);
2. Registration and unregistration
2.1 Register
To register a function-return probe, the user populates the following
fields in a kretprobe object and calls register_kretprobe() with the
kretprobe address as an argument:
kp.addr - the function's address
handler - this function is run after the ret instruction executes, but
before control returns to the return address in the caller.
maxactive - The maximum number of instances of the probed function that
can be active concurrently. For example, if the function is non-
recursive and is called with a spinlock or mutex held, maxactive = 1
should be enough. If the function is non-recursive and can never
relinquish the CPU (e.g., via a semaphore or preemption), NR_CPUS should
be enough. maxactive is used to determine how many kretprobe_instance
objects to allocate for this particular probed function. If maxactive <=
0, it is set to a default value (if CONFIG_PREEMPT maxactive=max(10, 2 *
NR_CPUS) else maxactive=NR_CPUS)
For example:
struct kretprobe rp;
rp.kp.addr = /* entrypoint address */
rp.handler = /*return probe handler */
rp.maxactive = /* e.g., 1 or NR_CPUS or 0, see the above explanation */
register_kretprobe(&rp);
The following field may also be of interest:
nmissed - Initialized to zero when the function-return probe is
registered, and incremented every time the probed function is entered but
there is no kretprobe_instance object available for establishing the
function-return probe (i.e., because maxactive was set too low).
2.2 Unregister
To unregiter a function-return probe, the user calls
unregister_kretprobe() with the same kretprobe object as registered
previously. If a probed function is running when the return probe is
unregistered, the function will return as expected, but the handler won't
be run.
3. Limitations
3.1 This patch supports only the i386 architecture, but patches for
x86_64 and ppc64 are anticipated soon.
3.2 Return probes operates by replacing the return address in the stack
(or in a known register, such as the lr register for ppc). This may
cause __builtin_return_address(0), when invoked from the return-probed
function, to return the address of the return-probes trampoline.
3.3 This implementation uses the "Multiprobes at an address" feature in
2.6.12-rc3-mm3.
3.4 Due to a limitation in multi-probes, you cannot currently establish
a return probe and a jprobe on the same function. A patch to remove
this limitation is being tested.
This feature is required by SystemTap (http://sourceware.org/systemtap),
and reflects ideas contributed by several SystemTap developers, including
Will Cohen and Ananth Mavinakayanahalli.
Signed-off-by: Hien Nguyen <hien@us.ibm.com>
Signed-off-by: Prasanna S Panchamukhi <prasanna@in.ibm.com>
Signed-off-by: Frederik Deweerdt <frederik.deweerdt@laposte.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Allow registration of multiple kprobes at an address in an architecture
agnostic way. Corresponding handlers will be invoked in a sequence. But,
a kprobe and a jprobe can't (yet) co-exist at the same address.
Signed-off-by: Ananth N Mavinakayanahalli <amavin@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.
Let it rip!
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